Ever since new, my truck (the one in my signature) only generates 0.25in of water column vacuum in the crankcase at idle. On the road, the max vac generated is about 0.8in wc. Previous vehicles I have owned have always generated about 2 to 4 in wc. I was wondering if this low vacuum is normal for the 4.3 engine.
Crankcase Vacuum -- only 0.25in.
- Thread starter George7941
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To add to my post.
Pinching off the fresh air from the air intake to the crankcase results in high vacuum - the needle climbed quickly to 15 in, at which point I chickened out and let fresh air in again. I pressurized the crankcase looking for leaks and only found two minor leaks - one at the base of the oi fill tube and one at the head of the dipstick. There is a small roll pin holding the plastic handle of the dipstick to the metal part of the dipstick and air was actually coming out thru the pin. I fixed both leaks, with no effect on the vacuum readings.
I have a Dwyer Magnehelic gauge which reads from 0 to 15 in wc. I used this gauge to measure the vacuum.
My PCV is just an orifice that is mounted on the intake manifold, it is not the typical PCV valve. I have not tried a new orifice yet.
Pinching off the fresh air from the air intake to the crankcase results in high vacuum - the needle climbed quickly to 15 in, at which point I chickened out and let fresh air in again. I pressurized the crankcase looking for leaks and only found two minor leaks - one at the base of the oi fill tube and one at the head of the dipstick. There is a small roll pin holding the plastic handle of the dipstick to the metal part of the dipstick and air was actually coming out thru the pin. I fixed both leaks, with no effect on the vacuum readings.
I have a Dwyer Magnehelic gauge which reads from 0 to 15 in wc. I used this gauge to measure the vacuum.
My PCV is just an orifice that is mounted on the intake manifold, it is not the typical PCV valve. I have not tried a new orifice yet.
The vacuum readings are taken from the dipstick tube. I am thus measuring the vacuum in the crankcase, which is why we are dealing with inches of water column. With intake manifold we would using either psi or inches of mercury column.
just out of curiosity, why measure crankcase vacuum?
Crankcase vacuum measures the performance of the PCV system. As long as the PCV is working properly the crankcase will be under a small vacuum.
In my case I have been chasing a "high Si value in UOA" problem ever since the truck was new and I still have not found a cause. I get 30ppm over a 4k mi OCI. Wear metals are normal.Truck is at 26k miles now. I thought perhaps I had a crankcase air leak but that does not seem to be the case. I cannot find any leaks in the air intake ducting or the intake manifold. Air filter has been replaced.
In my case I have been chasing a "high Si value in UOA" problem ever since the truck was new and I still have not found a cause. I get 30ppm over a 4k mi OCI. Wear metals are normal.Truck is at 26k miles now. I thought perhaps I had a crankcase air leak but that does not seem to be the case. I cannot find any leaks in the air intake ducting or the intake manifold. Air filter has been replaced.
That sounds normal and good!
You have a bit of neg pressure that raises when you close the inlet.
This is what you want - I don't see a problem.
You have a bit of neg pressure that raises when you close the inlet.
This is what you want - I don't see a problem.
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Excellent (attempted) detective work!
I'm trying to lock down a similar problem. Went over everything. I sniped an ultrasonic leak detector off of Ebay in an attempt to find a leak. At idle ..you can get some upticks in the chirping ..but nothing substantial. The most frequent point of increased leakage (if you could call it that) is the injector ports.
I'm trying to lock down a similar problem. Went over everything. I sniped an ultrasonic leak detector off of Ebay in an attempt to find a leak. At idle ..you can get some upticks in the chirping ..but nothing substantial. The most frequent point of increased leakage (if you could call it that) is the injector ports.
Originally Posted By: George7941
Crankcase vacuum measures the performance of the PCV system. As long as the PCV is working properly the crankcase will be under a small vacuum.
In my case I have been chasing a "high Si value in UOA" problem ever since the truck was new and I still have not found a cause. I get 30ppm over a 4k mi OCI. Wear metals are normal.Truck is at 26k miles now. I thought perhaps I had a crankcase air leak but that does not seem to be the case. I cannot find any leaks in the air intake ducting or the intake manifold. Air filter has been replaced.
Si, from what I have read, is used in lube when building the engine. Id get a few more OCIs in to see if you have an issue. Your engine, at your miles, is just getting done with "break in". So the next 2-3 OCI should tell the story.
I assume you are using a paper OEM air filter, and the air box is nice and tight.
Crankcase vacuum measures the performance of the PCV system. As long as the PCV is working properly the crankcase will be under a small vacuum.
In my case I have been chasing a "high Si value in UOA" problem ever since the truck was new and I still have not found a cause. I get 30ppm over a 4k mi OCI. Wear metals are normal.Truck is at 26k miles now. I thought perhaps I had a crankcase air leak but that does not seem to be the case. I cannot find any leaks in the air intake ducting or the intake manifold. Air filter has been replaced.
Si, from what I have read, is used in lube when building the engine. Id get a few more OCIs in to see if you have an issue. Your engine, at your miles, is just getting done with "break in". So the next 2-3 OCI should tell the story.
I assume you are using a paper OEM air filter, and the air box is nice and tight.
rg200amp -- The airbox is nice and tight and the original Delco filter was replaced with a (paper)Wix with no change in Si readings. All indications are that the high Si readings is from the fact the the engine is still relatively new. I did find another Bitoger with high Si from a 4.3l.
http://www.bobistheoilguy.com/forums/ubb...true#Post246507
Gary Allan -- Are you satisfied with your ultrasonic detector? What brand is it and how much did you pay? I had always assumed that these detectors could only be used on the side the leak is going into i.e. the low pressure side, but your post indicates otherwise. Also, are you saying that the detector indicated possible leaks past the injectors on your vehicle when you tested it?
http://www.bobistheoilguy.com/forums/ubb...true#Post246507
Gary Allan -- Are you satisfied with your ultrasonic detector? What brand is it and how much did you pay? I had always assumed that these detectors could only be used on the side the leak is going into i.e. the low pressure side, but your post indicates otherwise. Also, are you saying that the detector indicated possible leaks past the injectors on your vehicle when you tested it?
Originally Posted By: George7941
rg200amp -- The airbox is nice and tight and the original Delco filter was replaced with a (paper)Wix with no change in Si readings. All indications are that the high Si readings is from the fact the the engine is still relatively new. I did find another Bitoger with high Si from a 4.3l.
http://www.bobistheoilguy.com/forums/ubb...true#Post246507
Do three more OCIs then get a used oil analysis. I think you will see the SI in a low normal level then.
Very nice engine. There a blast with 4x4 in the snow!
rg200amp -- The airbox is nice and tight and the original Delco filter was replaced with a (paper)Wix with no change in Si readings. All indications are that the high Si readings is from the fact the the engine is still relatively new. I did find another Bitoger with high Si from a 4.3l.
http://www.bobistheoilguy.com/forums/ubb...true#Post246507
Do three more OCIs then get a used oil analysis. I think you will see the SI in a low normal level then.
Very nice engine. There a blast with 4x4 in the snow!
What problem?
Originally Posted By: mechtech2
What problem?
High Si values in UOA.
What problem?
High Si values in UOA.
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